Generally, a brush cutter includes a motor, a rotary shaft connected to the motor and a head connected to the rotary shaft, and a cutting cord (mainly made of nylon) is radially extended from the head. Thus, such brush cutter can perform a brush cutting operation for cutting grass and the like using the cutting cord by rotating the head.
There is proposed a reel-winding type rotary cutter in which a reel for winding a cutting cord thereon is mounted on the head. For example, such reel-winding type rotary cutter is configured so that the cutting cord is pulled out from the reel by pressing the cutter against the ground or striking the head while it is rotating, or maximally increasing the rotation of the motor. However, the operation of pressing/striking may be dangerous as it causes scattering of small stones, and the operation of maximally increasing the rotation may cause the increase in weight as it requires the complex structure. Further, above-mentioned operations not only may impart large loads on the motor and the cutter encounter but also may result in the unstable cord pull-out operation.
In view of above, there is also proposed another reel-winding type rotary cutter which is configured so that the cutting cord is automatically pulled out from the reel when the cutting cord is worn and shortened during the brush cutting operation. For example, the cord is automatically pulled out when it becomes short due to the change of the centrifugal force. Thus, the above-mentioned operations of pressing/striking or increasing the rotation are not necessary, and the cord pull-out operation can be performed simply and safety. On the other hand, the number of components of the head is increased. Thus, the structure of the head is complicated, thereby increasing the cost of the cutter. Further, since the head becomes heavy, the cutter also becomes heavy.
In view of above, there is proposed a directly-attaching type (non reel-winding type) rotary cutter in which a reel for winding a cutting cord thereon is not provided, but a cutting cord of a suitable length is directly attached to the head and is replaced when it becomes short by being worn. For example, US-2008-155837-A proposes a directly-attaching type rotary cutter in which a head main body (for example, a head 100) is constituted of a case (for example, a lower cover 106) and a cover (for example, an upper cover 105). A cord guide hole through which a cutting cord is inserted is defined in the head main body. A U-like-shaped pressure member (for example, a button 210 and a locking blade 300) with cord penetration holes (for example, clamp slots 305, 306) is incorporated within the head main body so as to be slidable in a direction perpendicular to the cord guide hole against a spring (for example, a spring 220). A nut (for example, an arbor 420) for connecting a rotation drive shaft is incorporated within the central portion of the head main body so as to block between the cord penetration holes of the pressure member. The nut also has a penetration hole (for example, a channel hole 199).
To attach the cutting cord onto the head main body, first, the pressure member is pushed inwardly of the head main body against the spring so that its cord penetration holes are aligned with the cord guide hole of the head main body and the penetration hole of the nut. Then the cutting cord is inserted into the cord guide hole of the head main body, the cord penetration holes of the pressure member and the penetration hole of the nut, so that two end portions of the cord are projected outwardly of the head main body. Next, the pressure onto the pressure member is released so as to be pushed back outwardly of the head main body by the spring. Thus, the cord penetration holes of the pressure member are shifted from the cord guide hole of the head main body and the penetration hole of the nut, and the cutting cord is fixed to the head main body in the bent state.
The above-mentioned directly-attaching type rotary cutter has the following disadvantages.
(1): Since the diameter of the cord guide hole defined in the head main body and the diameter of the cord penetration holes formed in the pressure member are determined, it is not possible to cope with a cutting cord of various thicknesses (diameters).
(2): To attach or remove the cutting cord onto or from the head main body, since it is necessary to move the pressure member to align its cord penetration holes with the cord guide hole, required time and labor are increased.
(3): Since the U-like-shaped pressure member is incorporated at one side of the head main body, the weight balance of the head main body is deteriorated, and the vibration may be caused.
(4): Since the cutting cord is held at the cord penetration holes of the pressure member, the holding force of the cutting cord may not be sufficient, and the cutting cord may be moved or even removed from the head main body due to the centrifugal force during the brush cutting operation.